Fix OnReturn secondary resource pipeline for HasOne relationships

src/Examples/JsonApiDotNetCoreExample/Definitions/PassportHooksDefinition.cs

@@ -32,6 +32,11 @@ public override void BeforeImplicitUpdateRelationship(IRelationshipsDictionary<P
             resourcesByRelationship.GetByRelationship<Person>().ToList().ForEach(kvp => DoesNotTouchLockedPassports(kvp.Value));
         }
 
+        public override IEnumerable<Passport> OnReturn(HashSet<Passport> resources, ResourcePipeline pipeline)
+        {
+            return resources.Where(p => !p.IsLocked);
+        }
+
         private void DoesNotTouchLockedPassports(IEnumerable<Passport> resources)
         {
             foreach (var passport in resources ?? Enumerable.Empty<Passport>())

src/JsonApiDotNetCore/Hooks/Internal/ResourceHookExecutorFacade.cs

@@ -125,10 +125,10 @@ public object OnReturnRelationship(object resourceOrResources)
                 return _resourceHookExecutor.OnReturn(resources, ResourcePipeline.GetRelationship).ToArray();
             }
 
-            if (resourceOrResources is IIdentifiable identifiable)
+            if (resourceOrResources is IIdentifiable)
             {
-                var resources = ToList(identifiable);
-                return _resourceHookExecutor.OnReturn(resources, ResourcePipeline.GetRelationship).Single();
+                var resources = ToList((dynamic)resourceOrResources);
+                return Enumerable.SingleOrDefault(_resourceHookExecutor.OnReturn(resources, ResourcePipeline.GetRelationship));
             }
 
             return resourceOrResources;

test/JsonApiDotNetCoreExampleTests/Acceptance/ResourceDefinitions/ResourceDefinitionTests.cs

@@ -241,6 +241,29 @@ public async Task Article_Through_Secondary_Endpoint_Is_Hidden()
             Assert.DoesNotContain(toBeExcluded, body);
         }
 
+        [Fact]
+        public async Task Passport_Through_Secondary_Endpoint_Is_Hidden()
+        {
+            // Arrange
+            var person = _personFaker.Generate();
+            person.Passport = new Passport(_dbContext) {IsLocked = true};
+
+            _dbContext.People.Add(person);
+            await _dbContext.SaveChangesAsync();
+
+            var route = $"/api/v1/people/{person.Id}/passport";
+
+            // Act
+            var response = await _client.GetAsync(route);
+
+            // Assert
+            var body = await response.Content.ReadAsStringAsync();
+            Assert.True(HttpStatusCode.OK == response.StatusCode, $"{route} returned {response.StatusCode} status code with body: {body}");
+            var document = JsonConvert.DeserializeObject<Document>(body);
+            Assert.Null(document.Data);
+
+        }
+
         [Fact]
         public async Task Tag_Is_Hidden()
         {